In recent years, so-called radio frequency Identification (RFID) systems that use non-contact type IC cards or IC tags have been introduced into automatic gates at railway stations, entrance/exit security systems, electronic money systems, and the like. As FIG. 1 schematically shows, the RFID system comprises a non-contact type IC card 100 and a reader/writer 101. The reader/writer 101 can write data into, and read data from, the IC card 100. In the RF system, when a loop antenna 102 provided on the reader-writer 101 radiates a magnetic flux, the magnetic flux is magnetically coupled with a loop antenna 103 provided on the IC card 100, in accordance with the principle of electromagnetic induction. Thus, communication is performed between the IC card 100 and the reader/writer 101.
In the RFID system, the user need not insert the IC card into the reader/writer or set the IC card into contact with the metal contact point provided on the reader/writer as is required in the conventional contact-type IC card system, and data can be easily and fast written and read into and from the IC card. Since the reader/writer 101 supplies power to the IC card 100 by virtue of electromagnetic induction, the IC card 100 need not incorporate a power supply such as a battery. The RFID system therefore can provide IC cards that are simple in configuration and, inexpensive and reliable.
However, the IC card may fail to communicate with the reader/writer if it incorporates an IC tag having communication frequency of 13.56 MHz. That is, the IC tag is influenced by any metal member that lies near the IC card. In the communication achieved at 13.56 MHz by virtue of electromagnetic induction, the IC tag is influenced by any metal member that exists near it, inevitably changing inductance. The change in inductance results in a shift of the resonance frequency or a change in the magnetic flux. As a result, no power can be attained.
In the RFID system described above, to ensure he communicable range between the IC card 100 and the reader/writer 101, the IC card 100 needs to have the loop antenna 103 that can emit an electromagnetic field having a sufficient magnetic field intensity.
A technique that can reduce the influence a metal housing imposes on the loop antenna is known, other than the technique of arranging the loop antenna in an open space. Jpn. Pat. Appln. Laid-Open Publication No. 2001-331772, for example, discloses an antenna apparatus for use in IC cards. This antenna apparatus has a plate of magnetic material, which reduces the influence of any metal member.